Γ-ray Decay Research Articles

Large deformation in A ∼ 170 nuclei at high excitation energies

The γ-ray decay of the giant dipole resonance was measured in coincidence with fission fragments following the fusion reaction 16O+ 159Tb forming 175Ta at 123.4 MeV excitation energy. A large splitting of the giant dipole resonance (GDR) energies in the compound system was observed corresponding to a large deformation of β=0.55.

Pi0-decay gamma-ray emission from winds of massive stars

We propose that the chaotic stellar winds from massive stars are potential π 0 -decay γ-ray sources. A small fraction of the thermal ions is first-order Fermi accelerated to high energies by the shocks embedded in the highly unstable radiatively driven winds. These particles interact with the thermal ions to produce γ-rays peaked around 0.1 GeV via π 0 -decay. When the mass-loss rate of an early-type star is high enough, the wind becomes opaque to the ion-ion interactions and a substantial fraction of the nonthermal ions' energy is emitted in γ-rays

Neutral pion production in the reactions 16O+ 27Al, 58Ni, 208Pb at Elab=95 MeV/nucleon

The production of neutral pions has been studied in the 16O+ 27Al, 58Ni, 208Pb reactions at 95 MeV/nucleon. Inclusive pion differential distributions dσ dp t , dσ dT π , and dσ dΩ have been measured by detecting the two-pion decay γ-rays in a setup of 8 lead glass Cherenkov detector telescopes. The data are discussed in the framework of a moving thermal source model. It is shown that the shape of the pion energy spectra is better described if mean field effects on the primary pion-production cross section and pion reabsorption are included in the calculation.

Total cross sections for the ppπ 0 channel in the inelastic pp interaction

Total cross sections for the reaction p+ p→ p+ p+ π 0 have been measured for proton incident energies ranging from 480 to 560 MeV in 20 MeV steps, by detecting the decay γ-rays of the π 0 emitted at forward angles. Isoscalar partial cross sections (σ 01) are extracted by comparison to the known total cross sections of the n+ p→ n+ n+ π + measured at the same incident energies. No signal in the energy dependence of the π 0 production excitation function due to possible narrow, isovector dibaryon resonance is noticeable in the data.

Spin dependence of the giant dipole resonance in Gd isotopes

The shape evolution of the Gd nuclei produced by the 124Sn+ 30Si reaction at a beam energy of 150 MeV has been studied as a function of spin by measuring the γ-ray decay of the giant dipole resonance. The nuclear deformation was extracted from the spectral shape and, independently, from the angular distribution with respect to the spin axis. Both measurements reveal that these nuclei remain prolate, with an increase in deformation as the spin increases. Sum-energy and multiplicity distributions have also been measured as a function of γ-ray energy.

Advances in germanium detector fabrication

Each radionuclide is able to emit radiation of a characteristic type and energy which is unique to that given radioisotope. The use of germanium detectors in γ-ray spectroscopy provides a mechanism for the interpretation of this unique signature. Indeed, γ-ray decay studies can yield information on all the properties of discrete states of nuclei (see Renaissance of nuclear spectroscopy by John Sharpey-Schafer p31).

Excitation and superradiance of isomeric nuclei in a laser plasma in a high-intensity laser radiation field

A theoretical investigation is made of deexcitation of isomers via a nearby level and of excitation of atomic nuclei to lower isomeric states in a hot plasma. An analysis is made of the problems of plasma diagnostics in laser controlled thermonuclear fusion under conditions which are difficult to study by traditional methods. A new approach to pumping of Mossbauer transitions is proposed. It is shown that a γ-ray superradiance wave may be emitted by a system of such nuclei. An analysis is made of the mechanism of acceleration of γ-ray decay of isomers due to a direct interaction between high-intensity laser radiation and nuclei involving mixing of ordinary nuclear states and of giant resonances.

The g-factor of the K=25 isomer in 182Os

The g-factor of the K= I=25 isomer in 182Os has been measured by observing the angular precession of the decay γ-ray angular distribution in an external magnetic field as g=+0.425 (8). This result is compared with predictions based on experimental g-factors of single-particle Nilsson orbitals in this mass region.

Proton-generated MeV gamma-rays from supernova 1987A

view Abstract Citations (5) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proton-generated MeV Gamma Rays from Supernova 1987A Stanev, Todor ; Vankov, H. P. Abstract We have calculated the time evolution of MeV φ^0^ decay γ-rays that is due to cascading in the material of the supernova shell. The cascading significantly alters the γ-ray production spectrum, generates γ-ray fluxes in the 1-10 MeV range and creates strong signatures that are characteristic of the overall column density and the structure of the shell. For cosmic-ray luminosity 10^39^ erg s^-1^ the γ-ray fluxes above 3 MeV are well above the GRO sensitivity. Publication: The Astrophysical Journal Pub Date: August 1989 DOI: 10.1086/167752 Bibcode: 1989ApJ...343..828S Keywords: Gamma Ray Astronomy; Particle Acceleration; Supernova 1987a; Compton Effect; Light Curve; Monte Carlo Method; Scattering Cross Sections; Astrophysics; GAMMA RAYS: GENERAL; PARTICLE ACCELERATION; STARS: INDIVIDUAL ALPHANUMERIC: SN 1987A; STARS: SUPERNOVAE full text sources ADS | data products NED (2) SIMBAD (1)

Decay of neutron deficient Eu, Sm and Pm isotopes near the proton drip line

The β-delayed proton and γ-ray decays of the two new isotopes 134,135Eu and of 136Eu, 134,135,136Sm, 134,135,136Pm and 135Nd were studied This is the flrst observation of β-delayed proton decay in europium isotopes. On-line mass separation and X-ray coincidences were used for isotope identification. Half-lives of 0.5 ±0.2 s and 1.5 ±0.2 s were measured for 134Eu and 135Eu respectively. For 136Eu evidence for two isomers with half-lives of 3.7 ±0.3 s and ~3.0 s was obtained. Betadelayed proton emission was assigned to the decays of 134Eu, 135Sm and 136Eu based on proton K X-ray coincidences and mass separation. Proton branching ratios of (9±3) × 10 −4 for 136Eu and (2±1) × 10 −4 for 135Sm were measured. Beta-delayed proton emission to the 0 + ground and to the 2 + excited states in 134Nd was observed following the 135Sm decay. The 135Eu activity was identified by Sm K α X-rays from its electron-capture decay, and one γ-ray was assigned to this decay. Fast allowed Gamow-Teller 0 + → 1 + β-transitions to the 118.9keV level in 134Pm and 114.4keV level in 136Pm were identified. The low-spin β-decays of 136Pm and 135Nd were studied without significant interference from the high-spin decays, and decay schemes were constructed for 134,135,136Sm, 134,135,136pm and 136Eu

Particle–core multiplets in 89Y

The 89Y nucleus has been formed in its excited states via the 87Rb(α, 2n) reaction at incident energies 24-34 MeV. The γ-ray decay of the states has been studied by measuring γ-γ-t coincidences, angular distributions and relative excitation functions. The experimental results from the present investigation are in general agreement with the former studies, however some corrections in the level scheme have been introduced. Eight new levels with spins up to around 31/2ℏ have been observed. The uppermost levels have been arranged into a rotational-like sequence suggesting a nuclear shape change. Using our and previously known data we have tried to locate and calculate the members of the 1g9/2 ⊗ core multiplet. The present results are compared with the semi-empirical shell model and the particle-core weak coupling description.

The 25Mg(p, γ)26Al reaction; branchings, energies and lifetimes

The γ-decay has been measured of 75 25Mg(p, γ)26Al resonances in the Ep = 0.31–1.84 MeV region with Ge detectors at 90° and 55°, the latter in a Compton suppression shield. Several of these resonances had not been observed previously and of about half the decay had not been measured. The spectra have been corrected for summing effects, for the instrumental tails of lower-energy resonances, for the Breit-Wigner tails of neighbouring broad resonances, and for direct capture. On the average about 29 primaries are observed per resonance (with a maximum of 48); 74 primaries are of the resonance → resonance type. Altogether 109 secondary states are excited in the decay, of which 50 had been seen in previous (p, γ) work. The total number of observed decay γ-rays from non-resonance levels amounts to 548, with a maximum number of branches per level of 20. Accurate energies have been measured for all states. The errors amount to ΔEx = 0.03–0.26 keV for the non-resonance levels and to 0.04–0.4 keV for the resonances (with ΔEx = 2 keV for four very broad resonances). As a byproduct lifetimes (or lifetime limits) have been measured from the observed Doppler shifts for 32 levels for which no previous measurements existed.

Gamma-ray decaying states at high excitation in 20Ne

A search has been made for high-lying states in 20Ne which decay by γ-ray emission. The states were populated via the 12C( 12C, α) 20Ne reaction at a beam energy of 37.1 MeV. A technique which allowed the measurement of γ-ray emission probabilities down to less than 1% was employed. In addition to previously known γ-ray emitting states, states at 11.89, 12.01, 12.10, 12.17 and 12.38 MeV were found to have observable γ-ray decay modes.

Calculated uncertainties of absolute γ-ray intensities and decay branching ratios derived from decay schemes

This paper presents analytical methods for calculating uncertainties of absolute γ-ray intensities and decay branching ratios derived from decay schemes. The equations have been derived with standard mathematical error-propagating techniques, using first-order approximations in Taylor series expansions of absolute γ-ray intensities.

A high-resolution 62Ni(p, γ)63Cu study

The γ-ray decay of ten selected 62Ni(p, γ)63Cu resonances in the proton-energy range Ep = 1.15–1.70 MeV has been measured with a Compton suppression spectrometer. Analysis of these measurements provides detailed information about the decay of about one hundred bound states. This includes more than fifty levels, which have up to now not been observed.Excitation-energy measurements, necessary to study the very complicated decay schemes, are performed with an average uncertainty of 30 ppm.Resonance energies with a precision of typically 0.1 keV have been determined by comparing the 62Ni(p, γ) yield curves with 27Al(p, γ) resonance yield curves. The reaction Q-value is found to be Q = 6122.35 ± 0.09 keV.Shell-model calculations have been performed in a 2p32, 1f52and 2p12 configuration space with a closed 56Ni core. The calculated excitation energies agree quite well with the experimental values.

Pn-values of 94Rb and 95Rb measured by a β−γ spectroscopic method

The delayed-neutron emission probabilities ( P n-values) of 94Rb and 95Rb have been measured as 9.73 ± 0.62 and 8.60 ± 0.57%, respectively, by a β−γ spectroscopic method utilizing the on-line isotope separator KUR-ISOL. This method can be usefully applied if a pure isotopic and mass-separated ion beam is available and the absolute emission probabilities per decay of main γ-rays emitted from relevant nuclides are well-established.

The decay of188Re

The γ-ray spectra of188Re decay have been studied by using two Ge/Li/ spectrometers and a three parameters /E-E-T/ List coincidence system. The energies and relative intensities of 52 γ-rays and cascade relations of 14 γ-rays are determined. Ten new γ-rays: 155 /633–478/, 984, 1096, 1463, 1332, 1530, 1574, 1810, 1867, and 1937 keV have been identified. The 155 /633–478/ transition is confirmed and its relative intensity is estimated by means of coincidence experiment. 24 levels of188Re are assigned. Among those, 6 levels are first put into the decay scheme of188Re. In addition to 1443 keV and 1937 keV levels, 1685, 1729 and 1965 keV levels are also observed in the decay of188Ir and other reaction studies. The 1948 level is recently suggested in the190Os/p, t/188Os reaction. The 486 keV and 811 keV γ-transitions are also put into the level scheme of188Re. The β− decay branching ratio is deduced.

Evaluation of Decay Heat in Fusion Experimental Reactor

Decay heat in the blanket and shield of the Fusion Experimental Reactor (FER) was calculated using a newly developed radioactivation calculation code system THIDA-2. The decay heat at various time periods after shutdown were calculated. The decay heat level in the FER blanket was found to be at least one order of magnitude lower than in fission reactors at all time periods after shutdown. The necessity of following the transport of decay γ-rays in obtaining the detailed distribution of decay heat in the blanket was demonstrated. The validity of the γ-ray kerma factors used in the evaluation was also shown.

High resolution study of the γ-ray spectrum following228Ac decay

The decay of228Ac has been reinvestigated by means of high resolution HPGe detectors. Accurate energies and intensities of 242 γ photons were measured, of which 80 were found for the first time.

Measurement of a highly retarded α-particle decay in 20Ne

The partial widths for α-particle and γ-ray decay of the second 2 + T = 1 level in 20Ne at 12.22 MeV have been measured. The reaction 19F( 3He, d) 20Ne was employed, with deuterons detected in singles and in coincidence with γ-rays from the decay of the 12.22 MeV level. The coincidence efficiency was determined using the 100% γ-decay of the 10.89 MeV 3 + T = 1 level. The ratio of the γ-decay width to the total width of the 12.22 MeV level was measured to be 0.88 ±0.05, which combined with a recent 16 O(α, γ) 20Ne measurement yields a very small α-particle width of 0.32±0.06 eV. This result is also of relevance to the radiative decay of the 18.43 MeV 2 + T = 2 level in 20Ne, and confirms a large discrepancy between the measured γ-decay width of the 2 + T = 2 level and the predictions of the shell model.